weight gain on steroids

My doctor put me on a steroid plus pain medication for three ruptured discs I received in a head on collision. Is it normal to gain weight on steriods? For some reason I have gained 9 LBS in ONE WEEK since being on these!!!! If so, why is this? will it be easy to take off once I go off them? This is terrible, not helping me feel any better, that is for sure.